Copper fouling can be a witch to remove. I start out with Hoppes #9 to get rid of all the powder fouling, and then follow up with Copper Cleaner from Pro-Shot Products. There are many other products on the market, but I have used these for years. Sometimes I will use some JB bore paste to speed things up. It sometimes takes me all day to get a rifle bore clean if I have shot very many rounds through it. My ARs in particular are very time consuming to clean. But, I figure it is easier to clean them everytime than to allow the copper to build up.
Sweets is one of the best copper removes . Takes 10 mins to work , the patch will turn blue till copper is removed . Don't leave in bore over 1/2 hour . I store gun with Hoppe left in bore muzzle down on white rag , if it turns green in couple days you still have copper in it . Do the Sweets again then the Hoppes again . Kroil is another one is good for copper and lead both , I always store gun with Hoppes in it .